1. Field of the Invention
The present invention relates to a spinning frame, such as a flyer frame or fine spinning frame, provided with two AC (alternate current) motors for operating different parts of the spinning machine, and more particularly, a device for controlling the different AC motors upon a power failure, without a breakage of a roving or thread at respective spinning portions of the spinning frame.
2. Description of the Related Art
Known in a prior art is a flyer frame having a first AC motor imparting a rotational movement to drafting parts and flyers, and a second AC motor independent from the first AC motor and used for imparting a variable rotational movement to bobbin wheels. Inverters are provided for the first and second AC motors, respectively, for obtaining a desired rotational speed control of these AC motors. This type of flyer frame can eliminate a conventional cone drum type speed control mechanism fed by a single electric motor for controlling the varied speed of the bobbin. See Japanese Unexamined Patent Publication No. 63-264923 and Japanese Unexamined Patent Publication No. 3-40819. In the first patent ('923), a controller executs a calculation of a bobbin rotational speed from a detected spinning speed and the diameter of a bobbin including a wound roving on the bobbin, and the second AC motor is controlled by an inverter so that the calculated bobbin rotational speed is obtained. In the second patent ('819), a rotating angle of a front roller of a drafting part and the diameter of a bobbin including the wound roving are detected, and a controller operates the AC motor so that a desired rotating angle of the bobbin is obtained. Furthermore, the inverter controls an accelerated or decelerated rotation of the AC motors, upon a start or stoppage when a full bobbin state is obtained.
In such a type of flyer frame, wherein two or more independent motors are provided for rotating different parts of the flyer frame, upon the occurrence of a power failure, rotating parts connected to the respective AC motors continue to rotate for a while due to the inertial moments of the respective rotating parts, which have usually different values. As a result, before a completely stoppage after the commencement of the occurrence of the power failure, the rotating parts connected to one of the AC motors, i.e., the drafting parts and flyers, having a larger inertia value take a longer time to stop than the other rotating parts, connected to the other AC motor, i.e., the bobbin wheels, having a smaller inertia value. As a result, a relationship of rotational speeds between the parts connected to the first AC motor and the part connected to the second AC motor after the power failure becomes different from that desired during normal operation, which causes the tensions of rovings to be outside a desired range, and thus a desired winding of the rovings is not obtained, and accordingly, sometimes almost of all the rovings are simultaneously broken at the respective spinning position of the flyer frame.
To obviate such a problem arising upon the occurrence of the power failure, Japanese Unexamined Patent Publication No. 60-155729 and Japanese Unexamined Patent Publication No. 2-221424 discloses a concept whereby, upon an occurrence of a power failure, from the rotating parts having the larger inertia connected to the first AC motor, via the inverter, a regeneration electric power is taken out and supplied to the second AC motor connected, via the corresponding inverted, to the rotating parts having the smaller inertia. A back-up battery is provided by supplying the control circuit for both of the inverters, so that the desired rotation of the first and second AC motors is obtained until the motors are completely stopped, even though a power failure has occurred.
The prior art system wherein the controller to the inverters of the first and second AC motors, respectively, is operated by the back-up battery suffers from a drawback in that frequent maintenance is required for a supplementation or exchange of a battery liquid, and the battery itself must be periodically replaced. Furthermore, an additional device is required for a charging thereof, which increases the overall cost.